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Trouble shooting
of a-stable multivibrator


Check the following when the a-stable multivibrator circuit does not operate well.
Failure is the base of success, then find the cause of the trouble.
That, there was a trouble, more the comprehension of the circuit deepens.

The circuit tester is done to about the voltage measurement mode 15V range. The black test stick is applied to the ground wire, and the red test stick is applied to 12 C each.
Is voltage changing cyclically ? ( Dose the voltage make a round trip 0V neighborhood and +5V neighborhood ? )


Yes	-	The multivibrator circuit is operating normally. Do the check of the light emitting diode circuit.
No	-	The multivibrator circuit is not operating. Do the check of the multivibrator circuit.

Is not it flickering in all of red, green, both ?

Flickering only red	-	The attachment of D4 is confirmed. Is not it attaching polarity conversely? The attachment of TR2 is confirmed. Are not the base and emitter opposite? Are the resistor of R5 and R6 attached correctly? Soldering of the above part is confirmed. Once again it tries to melt it. When the above is normal, the defectiveness of the part is conceivable. Does the voltage of 7J change? Yes : The defectiveness of D4 is conceivable. Although there is voltage but does not change : The defectiveness of TR2 is conceivable. No voltage : The defectiveness of D4 or R6 is conceivable. The voltage(+12V) is applied at 6L, R6 is normal.
Flickering only green	-	The attachment of D3 is confirmed. Is not it attaching polarity conversely? The attachment of TR1 is confirmed. Are not the base and emitter opposite? Are the resistor of R3 and R4 attached correctly? Soldering of the above part is confirmed. Once again it tries to melt it. When the above is normal, the defectiveness of the part is conceivable. Does the voltage of 7F change? Yes : The defectiveness of D3 is conceivable. Although there is voltage but does not change : The defectiveness of TR1 is conceivable. No voltage : The defectiveness of D3 or R4 is conceivable. The voltage(+12V) is applied at 6D, R4 is normal.
It does not flicker in all of both	-	The attachment of D3 is confirmed. Is not it attaching polarity conversely? The attachment of TR1 is confirmed. Are not the base and emitter opposite? The attachment of D4 is confirmed. Is not it attaching polarity conversely? The attachment of TR2 is confirmed. Are not the base and emitter opposite? Are the resistor of R3, R4, R5 and R6 attached correctly? Are The voltage(+12V) applied at 6D and 6L? Soldering of the above part is confirmed. Once again it tries to melt it. When the above is normal, the defectiveness of the part is conceivable. Does the voltage of 7J change? Yes : The defectiveness of D4 is conceivable. Although there is voltage but does not change : The defectiveness of TR2 is conceivable. No voltage : The defectiveness of D4 or R6 is conceivable. The voltage(+12V) is applied at 6L, R6 is normal. Does the voltage of 7F change? Yes : The defectiveness of D3 is conceivable. Although there is voltage but does not change : The defectiveness of TR1 is conceivable. No voltage : The defectiveness of D3 or R4 is conceivable. The voltage(+12V) is applied at 6D, R4 is normal.

Is the mounting of IC1 normal?

The position of pins become opposite in the drawing where you saw from the upper side(TopView) where saw from the lower side(Wiring face), then it is easy to misunderstand.


Are the mounting of D1, D2 normal? Is polarity correct?

Are the polarity of C5, C6 correct?

Even if the polarity of capacitor is opposite circuit operation does. Even with there is the possibility that capacitor destroys. Check due to a sense.
Actually, When it is mistaking the polarity of this capacitor, the possibility that is mistaking as be same even other capacitor is high. Even other capacitors check.


Are the mounting of R1, R2 normal?

Soldering of the above part is confirmed. Once again it tries to melt it.

In the case that the above is normal the defectiveness of the part is conceivable.
It is difficult work to find the defective part. You try to exchange it to the turn from the part that has the possibility of defectiveness.

(1) IC1 ( The socket is used, then it is easy to exchange )
(2) Diode D1 or D2
(3) Capacitor C5 or C6

( Almost defectiveness thinks with absent. It is although capacitance is come off when it is a old thing. )

(4) Resistor R1 or R2

( Almost defectiveness thinks with absent. You are very unlucky. )


It is very serious to exchange the part of (2), (3) or (4).
All soldering of the parts, component leads must be removed.
Carry out without causing the quick temper.

Is the mounting of IC2 normal?

In the case of 78L05, it confirms whether or not the attachment of the component lead is normal.
Possessed part with, in the case that it is using the 3 terminals regulator other than 78L05, the position of the component lead may differ by the supplier. Confirm with standard table etc.


Is the mounting of C4 normal? Is polarity correct?

When polarity is opposite capacitance will differ. Also, the capacitor has destroyed. Check due to a sense.
Actually, When it is mistaking the polarity of this capacitor, the possibility that is mistaking as be same even other capacitor is high. Even other capacitors check.


Soldering of the above part is confirmed. Once again it tries to melt it.